motion in one dimensionfac.ksu.edu.sa/.../lect2_ch_2_motion_in_one_dimension.pdfmotion in one...

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Chapter 2 Motion in One Dimension

Dr. Feras Fraige Physics I Version 1

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Lecture Content

•General problem solving strategy •Position, velocity, and speed (Average and instantaneous) •Acceleration •Motion diagrams •Constant acceleration motion


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Problem solving strategy


Conceptualise

Categorise

Analyse

Finalise

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Problem solving strategy (1) Conceptualise


•Think about and understand the situation (Diagrams, figures,

tables)

•Construct a movie in your mind of what is happening

•Make quick sketch to the problem

•Focus on numerical and algebraic information

•Look for key phrases (stops, start from rest, free falling)

•Focus on the expected result of solving the problem (What is

exactly the question is asking for?)

•Don’t forget to incorporate information from your own

experience and common sense (can the speed of an ordinary

car reach 1000 km/hr?)

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Problem solving strategy (2) Catagorise


•After you understand the problem, simplify the

problem. By removing non important details to the

solution.

•Categorise the problem, is it simple plug-in

problem? Or you need to think and analyse more

deeply.

•Have you seen this problem before? Do u solve

similar problem before?

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Problem solving strategy (3) Analyse


•Select relevant equations to solve the problem

•Use algebra and Calculus to solve for the

unknown parameters

•Calculate the result and round it to the appropriate

significant figures.

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Problem solving strategy (4) Finalise


•This is the most important part.

•Examine the numerical result, Does it have the

correct unit?

•Does it meet you expectations of you

conceptualisation in stage 1

•Does it make sense?

•Think about how this problem compares with the

other you already solved before.

•Is it new problem you didn’t solve before? Make it

as a model for next problems

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Motion


•Study the kinematics (motion in space and time)

of particles (having mass and negligible size)

without studying the cause of motion.

•Motion types: translational, rotational, and

vibrational motions.

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Position •If particle position in space is know at all time, the motion can be evaluated. •Position is the location of particle in space at certain time and usually with respect to a chosen reference.


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Position – time graph •If particle position in space is know at all time, the motion can be evaluated. •Position is the location of particle in space at certain time and usually with respect to a chosen reference.


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Displacement


•Displacement is defined as the change (Δ) in

particle position during time interval.

•Initial position is xi and final position is xf ,

displacement = Δx = xf – xi (can be positive or

negative)

•Distance is the length of the path travelled (always

positive).

•Distance is not the same as the displacement.

•Displacement is a vector, while distance is scalar.

•Examples

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Velocity •Average velocity is defined as ratio of the displacement (Δx) of a particle in a time interval ( Δt ). •The average velocity can be positive or negative. •Average speed is defined as the ratio of the distance of a particle to the time interval.


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Instantaneous Velocity •When the time interval becomes small, approaches zero, the limiting velocity is the instantaneous velocity

•We will use the term velocity to denote for instantaneous velocity •Instantaneous speed is the absolute value of the velocity.


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Example


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Acceleration


•Average accelerationis defined as ratio of the change in velocity (Δv) of a particle in a time interval ( Δt ). •Average acceleration can be positive or negative.

•The instantaneous acceleration is given by

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Graphical representation of position, velocity and acceleration

with time

Dr. Feras Fraige Physics I Version 1 20-6-07

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Example


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Constant acceleration motion (in one dimension)


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Example


A

B

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Example


(A) At maximum height vyB = 0, g = – 9.80 m/s2

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Example


(B) What due you expect (v, t, y)

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Example


(C) What do you think about the points A and C re time, position

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Example


(D) What do you think about the velocity

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Example


(E) What do you think about the velocity What if the building is 30 m high? What will Change?

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Kinematics equations derived from Calculus


How to find the position from the velocity graph?

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Special case 1: Constant velocity


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Special case 1: linear velocity (Constant acceleration)


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Kinematics equations


How to find the position, velocity from the acceleration mathematically? here ax is constant

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Kinematics equations


How to find the position, velocity from the acceleration mathematically? If ax is constant

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Example


The speed of a bullet as it travels down the barrel of a rifle toward the opening is given by v = ( – 5 x 107) t 2 + (3 x105) t, where v is in meters per second and t is in seconds. The acceleration of the bullet just as it leaves the barrel is zero. (a) Determine the acceleration and position of the bullet as a function of time when the bullet is in the barrel. (b) Determine how long the bullet is accelerated. (c) Find the speed at which the bullet leaves the barrel. (d) What is the length of the barrel?

a

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Example


The speed of a bullet as it travels down the barrel of a rifle toward the opening is given by v = ( – 5 x 107) t 2 + (3 x105) t, where v is in meters per second and t is in seconds. The acceleration of the bullet just as it leaves the barrel is zero. (a) Determine the acceleration and position of the bullet as a function of time when the bullet is in the barrel. (b) Determine how long the bullet is accelerated. (c) Find the speed at which the bullet leaves the barrel. (d) What is the length of the barrel?

b

c

d

motion in one dimensionfac.ksu.edu.sa/.../lect2_ch_2_motion_in_one_dimension.pdfmotion in one...

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